MicroRNAs (miRNAs) are a class of short non-coding regulatory RNA genes, which act as post-transcriptional regulators of gene expression (Lee & Ambros (2001) Science 294(5543):862-4; Lau, et al. (2001) Science 294(5543):858-62; Lagos-Quintana, et al. (2001) Science 294(5543):853-8). By binding to the 3′-untranslated region of target mRNAs, the ˜21-23 nucleotide-long miRNAs can trigger translational downregulation and/or increased degradation of mRNA of target genes (Bartel (2009) Cell 136(2):215-33). The recent explosion of miRNA research in biomedical sciences and particularly in cancer biology attests to their importance to human disease (Ventura & Jacks (2009) Cell 136(4):586-91; Sempere & Kauppinen (2009) In: Handbook of Cell Signaling. 2nd ed. Oxford: Academic Press, Bradshaw & Dennis (eds.) pg. 2965-81). High-throughput expression profiling of RNA extracted from whole tissue biopsies has provided short lists of miRNAs that could serve as useful biomarkers for early detection, diagnosis and/or prognosis of different types of cancer (Barbarotto, et al. (2008) Int. J. Cancer 122(5):969-77). Low levels of let-7, miR-34, miR-126, miR-145 and high levels of miR-21, miR-155, miR-221 have been frequently reported in association with breast, colorectal, gastrointestinal, lung, pancreas, prostate and/or thyroid cancer (Barbarotto, et al. (2008) supra; Volinia, et al. (2006) Proc. Natl. Acad. Sci. USA 103(7):2257-61).
Pancreatic ductal adenocarcinoma (PDAC) is the fourth leading cancer-related deaths in the US with an annual mortality of nearly 38,000, a median survival of 6-7 months and a five-year survival rate of 4 to 5% (Bilimoria, et al. (2007) Cancer 110(4):738-44). PDAC is characterized by aggressive local invasion, early lymphatic and hematogenous dissemination, and chemotherapeutic resistance (Preis & Korc (2010) Cancer Biol. Ther. 9(10):754-63). Tissue diagnosis is most often obtained by Endoscopic Ultrasound-Guided Fine Needle Aspiration (EUS-FNA) sampling of the pancreatic mass or other suspicious lesion (Kahl & Malfertheiner (2004) Dig. Dis. 22(1):26-31). Less than 20% of PDAC patients are candidates for surgical resection at diagnosis (Sener, et al. (1999) J. Am. Coll. Surg. 189(1):1-7; Lim, et al. (2003) Ann. Surg. 237(1):74-85). Despite improved survival with adjuvant chemoradiotherapy following resection, most patients eventually die of their disease (Herman, et al. (2008) J. Clin. Oncol. 26(21):3503-10; Corsini, et al. (2008) J. Clin. Onocol. 26(21):3511-6; Pipas, et al. (2001) Int. J. Radiat. Oncol. Biol. Phys. 50(5):1317-22). The tumor-associated antigen CA 19-9, which may be used adjunctively in the management of patients with PDAC following tumor resection to monitor disease recurrence, cannot predict the metastatic potential of tumor or patient survival following resection (Locker, et al. (2006) J. Clin. Oncol. 24(33):5313-27). Conventionally, no tissue biomarkers have been identified to guide therapeutic strategies or predict patient prognosis in PDAC.
The expression of several microRNAs, as determined by quantitative reverse-transcription PCR analysis (qRT-PCR), is altered in PDAC. Among others, miR-21, miR-10b, miR-155, miR-196a, miR-203, miR-210 and miR-221 levels are increased in PDAC by comparison with the normal pancreas (Greither, et al. (2010) Int. J. Cancer 126(1):73-80; Bloomston, et al. (2007) JAMA 297(17):1901-8; Szafranska, et al. (2008) Clin. Chem. 54(10):1716-24; Lee, et al. (2007) Int. J. Cancer 120(5):1046-54; du Rieu, et al. (2010) Clin. Chem. 56(4):603-12; Zhang, et al. (2009) World J. Surg. 33(4): 698-709; U.S. Pat. No. 7,670,840) whereas miR-375 and miR-148 levels are decreased in PDAC (Bloomston, et al. (2007) supra; Hanoun, et al. (2010) Clin. Chem. 56(7):1107-18). In general, these studies did not take into account the fact that PDAC is highly desmoplastic, and that the pancreatic tumor mass may include variable amounts of inflammatory cells and mast cells, degenerating acinar cells, proliferating ductal cells, foci of acinar to ductal metaplasia (ADM) and/or pancreatic intraepithelial neoplasia (PanIN), as well as many cancer-associated fibroblasts and stellate cells (Hezel, et al. (2006) Genes Dev. 20(10):1218-49). Therefore, the spatial expression of miRNAs in PDAC tissue is needed.